Various types of dryers and coolers for granular materials are known in the prior art. In one type, known as a fluidized bed, a cushion of air or hot gas is blown through a porous bottom floor plate of a container. As a result, the granular material in the container is floated to effect drying, heating, quenching, calcination, or some other function.
The fluidization process, however, has a number of drawbacks. For example, an extremely high volume of air is necessary in order to produce even fluidization. A high added pressure drop across the plate at the bottom of the container through which the air is blown is a consequence of using sufficient air in attempting to ensure good distribution. Non-fluidized pockets may, in any case, result, and consequent non-conveyed pockets and product damage, or even fire, can resultantly occur.
Design problems are also inherent in fluidized bed drying. The distributor floor plate design involves a balance between an excess of orifices and corresponding covering bubble caps (which would introduce inaccuracy of air distribution and prove very expensive), on the one hand, and an insufficient number of such orifices and cover caps (which would result in too great a pressure drop across the slab), on the other.
Additionally, fluidized bed drying involves significant time and expense investment in maintenance. Periodic cleaning of the floor plate orifices and cover caps must be performed, as well as periodic removal of scrap iron or wood. Apparatus must be provided to convey away stones from the bottom of the bed.
In a fluidized bed also, only some material will be fluidized and conveyed away from the bed. Only material light in weight, such as the grain, will be fluidized and conveyed up and over a final baffle that holds the fluid bed depth.
In an attempt to overcome these deficiencies of the fluidized bed, other apparatus have been developed. B.N.W. Industries of Mentone, Ind. has developed a product known as the BELT-O-MATIC. In this device, wet grain is fed onto an end of a continuous conveyor belt. The belt is porous and is disposed for movement of an upper run thereof in a direction so as to convey the inputted wet grain through a housing of the apparatus. The upper run of the belt travels over a multiplicity of rollers which support the weight of the belt and grain. The belt porosity is sufficient to permit the passage of heated air upwardly therethrough without significant restriction. Heated air is provided by a unit within the housing below the conveyor belt.
Such a device conveys granular material to be dried much more efficiently than does a fluidized bed. The costs incident to fluidization are much greater because of the increased power necessary to provide the conveying function in a fluidized bed.
Additionally, a moving belt serves to convey all materials out of the housing, unlike a fluidized bed wherein some materials will be caught by the final baffle. A belt conveyor requires little if any cleaning. In fact, the pores in the belt will be purged of occluding material and dust particles as the belt flexes over special cleaning sprockets.
While the BELT-O-MATIC is an improvement in some respects over fluidized bed drying, never-the-less, there are problems existent with this device. In a dryer/cooler device, it is important that a maximum amount of the granular material be worked. Because of the depth at which the layer of granular material is maintained, it frequently happens that even heating is not effected. This is so, because, once the grain is inputted to the device, it is not agitated in any manner.
It is to these deficiencies and dictates of the prior art that the present invention is directed. The present invention is an improved granular material contacting apparatus which more efficiently functions to effect processing of a granular material.